Development and preliminary validation of the Brief Self-Compassion Inventory

Research and clinical interest in self-compassion has grown due to its associations with physical and mental health benefits. Widely used measures of self-compassion have conceptual and psychometric limitations that warrant attention. The purpose of this project was to develop a new self-compassion measure, the Brief Self-Compassion Inventory (BSCI), and test its psychometric properties. We developed items for the BSCI based on theory, prior research, and expert and cancer patient feedback. The BSCI was then tested with adults diagnosed with breast, gastrointestinal, lung, or prostate cancer (N = 404). Confirmatory factor analysis suggested a unidimensional structure, and internal consistency reliability was excellent. Construct validity of the BSCI was established through its correlations with psychological variables hypothesized to be related to self-compassion, such as mindfulness, acceptance of cancer, and other coping strategies. Furthermore, measurement invariance testing of the BSCI indicated that it could be used across patients of varying genders, cancer types, and stages of illness. In conclusion, the 5-item BSCI was determined to be psychometrically sound and suitable for use with adults of varying genders, cancer types, and stages of disease. The measure warrants testing with other medical and nonclinical populations.


Introduction
In recent years, self-compassion and its associations with physical and psychological health have garnered attention [1]. Most studies of self-compassion have been conducted using the Self-Compassion Scale (SCS) or its short-form (SCS-SF) [1,2]. These scales include three facets, each with a positive and a negative dimension [2][3][4]. The first facet is self-kindness, defined as being gentle and compassionate towards oneself, versus self-judgment, which involves reacting harshly to inner experiences. The second facet is common humanity, a shared understanding of human suffering, versus isolation, the feeling that one is alone in one's imperfection or suffering. The third facet, mindfulness, refers to being aware of the present-moment experience of suffering while keeping such experiences in perspective. Thus, one avoids extremes of a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 theories of compassion and self-compassion [2][3][4]30,[34][35][36] and existing self-compassion measures [2,30,37], we decided to refrain from using negatively worded items and assess the same three positive facets of self-compassion as the SCS while updating the definition of mindfulness. Whereas the SCS mindfulness subscale refers to balanced awareness of present-moment experiences of suffering, the BSCI assesses mindful acceptance, defined as approaching ongoing thoughts and feelings with openness. These internal experiences are viewed as an everchanging and natural part of life. This conceptualization reflects typical definitions of mindfulness in the psychological literature [38][39][40]. We maintained Neff's [4] definitions of self-kindness and common humanity in our new measure and conceptualized the three facets of selfcompassion as highly correlated protective factors with respect to physical and mental health.
Our measure was tested in patients diagnosed with solid tumors. We first conducted an exploratory factor analysis (EFA) and a parallel analysis to assess the factor structure of our original 15-item Self-Compassion Inventory (SCI). We then conducted confirmatory factor analyses (CFAs) to test two different factor structures for the 15-item SCI, including a singlefactor model with an overall self-compassion factor (Model 1) and a hierarchical model with three factors indicating a higher-order overall self-compassion factor (Model 2). Model 1 was based on results of our EFA and parallel analysis, and Model 2 was grounded in aspects of Neff's conceptual model [4]. We then selected items to form the 5-item BSCI and conducted a CFA to determine whether it had the same factor structure as the SCI. We also evaluated the BSCI's internal consistency and construct validity. We expected moderate associations between the BSCI and both positive psychological variables (i.e., mindfulness, quality of life, peaceful acceptance of cancer, active coping, and progress in values-based living) and negative psychological variables (i.e., depressive symptoms, anxiety, rumination, denial, struggle with illness, psychological inflexibility, cognitive fusion, and obstruction in values-based living) based on theory [8,[10][11][12]. Additionally, we examined whether the BSCI had smaller correlations with negative psychological variables (e.g., anxiety, depressive symptoms, rumination) compared to the SCS-SF total score and smaller correlations with anxiety and depressive symptoms compared to negative items of the SCS-SF. Finally, we examined the measurement invariance of the BSCI across cancer stages, cancer types, and genders.

Generation of initial item pool
Initially, 12 items were generated based on a conceptual model of self-compassion (i.e., selfkindness, mindful acceptance, and common humanity) [4] and existing self-compassion measures. A five-point response scale was selected with choices ranging from 1 = "not at all" to 5 = "very much." The items were reviewed by three doctoral-level experts in self-compassion and mindfulness. Based on expert feedback and cognitive interviews with 10 cancer patients (see S1-S3 Appendices for cognitive interview methods and results), three items were added and other items were altered prior to psychometric testing. Expert and patient feedback primarily focused on wording changes to improve clarity. The preliminary measure for psychometric testing included 15 items.

Participants and procedures
All study procedures were approved by the Indiana University's institutional review board (IRB). Participants were adults with a diagnosis of breast, gastrointestinal, lung, or prostate cancer recruited from a public hospital, an academic cancer center, and affiliated clinics in Indianapolis, Indiana from February to October 2018. Eligible patients were identified through institutional cancer registries. They were either �3 weeks post-diagnosis of stage IV cancer or had completed active treatment �6 months ago for stage I or II cancer. Participants showed no evidence of severe cognitive impairment based on a cognitive screener [41]. To ensure representation of demographic subgroups based on the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) data [42], purposive sampling was conducted by race, ethnicity, and gender. Eligible patients received mailed recruitment packets followed by a phone call for eligibility screening and verbal informed consent, which the research assistant documented in writing. The IRB approved a verbal informed consent process for this minimal risk study because the research assistant was not approaching patients in person. The survey was administered either online through REDCap or a mailed paper copy per each participant's preference. Participants received a $25 gift card for completing the survey.

Measures
Except for the SCI and BSCI, all study measures have been previously tested with cancer populations with evidence of reliability and validity.

Demographic and medical information
Cancer information, age, and gender were retrieved from patients' medical records. Patients self-reported other demographics and whether they had been diagnosed with or treated for 12 medical comorbidities in the last three years [43].
Self-compassion (SCI/BSCI). The initial measure or SCI had five items for each potential subscale-self-kindness, common humanity, and mindful acceptance. Participants rated each item with reference to the past two weeks on a 5-point Likert scale ranging from 1 = "not at all" to 5 = "very much." This scale was selected to parallel Patient-Reported Outcomes Measurement Information System (PROMIS) measures [44]. All items were positively worded; thus, higher scores represented greater self-compassion. In follow-up analyses, five items were selected to form the BSCI.
Self-compassion (SCS-SF). The 12-item Self-Compassion Scale-Short Form (SCS-SF) [37] was also administered. The SCS-SF contains six subscales-self-kindness, self-judgment, common humanity, isolation, mindfulness, and over-identification-and a 5-point Likert scale with opposing anchors of "almost never" and "almost always." The six negatively worded items in the SCS-SF measure were reverse-scored, and all items were summed to compute a global self-compassion score.
Anxiety and depressive symptoms. The 4-item PROMIS Anxiety and Depression measures were used to assess anxiety and depressive symptoms, respectively [45,46]. Both measures use a 5-point Likert scale with responses ranging from "never" to "always." Quality of life. The McGill single item scale [47] was used to assess quality of life. Patients were asked to rate their overall quality of life, considering all aspects of their life, on an 11-point scale (0 = "very bad" to 10 = "excellent").
Mindfulness. Subscales of the Five Facet Mindfulness Questionnaire-Short Form (FFMQ-SF) [48] were used to assess mindfulness. The FFMQ-SF consists of five 3-item subscales: Observing, Describing, Acting with awareness, Nonjudging of inner experience, and Nonreactivity to inner experience. Items are rated on a 5-point Likert scale (1 = "never or very rarely true" to 5 = "very often or always true"). The latter three subscales were administered in our survey because they were most predictive of mental health and symptom outcomes in prior research with cancer survivors [49].
Psychological inflexibility. Psychological inflexibility was assessed with the 7-item Acceptance and Action Questionnaire-II (AAQ-II) [50]. Participants were asked to rate the degree to which painful thoughts and feelings interfered with daily life and coping on a 7-point Likert scale ranging from "never true" to "always true." Values-based living. The 10-item Valuing Questionnaire (VQ) [51] was used to assess obstruction and progress in values-based living. Half of the questionnaire's items are negatively worded (Obstruction subscale), and the other half are positively worded (Progress subscale). Respondents rated how true each item was for them on a 7-point Likert scale ranging from "not true at all" to "completely true." Cognitive fusion. The 7-item Cognitive Fusion Questionnaire (CFQ) [11] was used to assess cognitive fusion, or the tendency to become entangled in thoughts that lead to overregulation of one's behavior. The CFQ contains statements about participants' thoughts. Participants rated how true each statement was for them on a 7-point Likert scale ranging from "never true" to "always true." Acceptance of cancer. The 12-item Peace, Equanimity, and Acceptance in the Cancer Experience (PEACE) [52] measure was used to assess patients' acceptance of their cancer. The measure contains two subscales-Struggle with Illness (7 items) and Peaceful Acceptance (5 items). All items are rated on a 4-point Likert scale ranging from "not at all" to "to a large extent." Denial and active coping. Two of the 14 subscales from the Brief COPE [14]-Denial and Active Coping-were used to assess coping responses to cancer-related stress. Each subscale contains two items and uses a 4-point Likert scale (1 = "I haven't been doing this at all" to 4 = "I've been doing this a lot").
Rumination. The Rumination subscale of the Rumination-Reflection Questionnaire (RRQ) [13] was used to assess rumination. Participants rated their level of agreement with each item on a 5-point Likert scale ranging from "strongly disagree" to "strongly agree."

Data analyses
Preliminary analyses. Descriptive statistics were calculated to characterize patients' demographic and medical information and other characteristics. The data were also examined for normality, linearity, skewness, and kurtosis. Data were considered skewed and kurtotic using guidelines of >|3| and >|10|, respectively [53].
Psychometric testing of the SCI/BSCI. First, we examined whether items were performing poorly based on the following criteria: 1) low factor loadings (i.e., <0.40); 2) low item-total correlations (i.e., <0.30) [54]; 3) one category received less than 5% of responses; or 4) more than 80% endorsed the highest or lowest category (i.e., there is a ceiling or floor effect) [55]. We considered eliminating items based on these numerical criteria while maintaining coverage of the main facets of self-compassion-self-kindness, common humanity, and mindful acceptance.
EFA [56] and parallel analysis [57,58] were performed to examine the factor structure of the 15-item SCI in Mplus Version 8 [59] (see S4 Appendix for description of methods and results). Results suggested that there was one factor according to model fit information and interpretability of factor structures. We then conducted CFAs to test two models for the 15-item SCI, including a single-factor model with an overall self-compassion factor and a hierarchical model with three factors indicating a higher-order overall self-compassion factor. A description of the CFAs and tests of internal consistency reliability and validity for the SCI are found in the S4 Appendix.
Given evidence for the unidimensionality of the SCI, the five items with 1) the highest item-total correlations/loadings and 2) providing sufficient content coverage for the target construct were selected to form the BSCI. A single-factor CFA was performed to examine whether the BSCI was also unidimensional. The robust full information maximum likelihood estimation method (RFIML) was used for the CFA to account for the nonnormality of ordinal items and missing data [60]. RFIML has been shown to be an appropriate approach to dealing with ordinal missing data [60]. Eight percent of participants had missing observations on some of the items. Model fit was determined using several indices, including the chi-square test statistic, comparative fit index (CFI), root-mean-square error of approximation (RMSEA), and standardized root mean square residual (SRMR). Although model fit guidelines vary, acceptable model fit was defined as: (1) a non-significant χ 2 statistic; (2) CFI>0.90; (3) RMSEA<0.08; and (4) SRMR<0.06 [61]. Another popular approach to analyzing ordinal data is the weighted least squares mean and variance adjusted (WLSMV) method. We did not use WLSMV in this study because it could produce less accurate chi-square test statistics than RFIML given the presence of missing data [62].
Internal consistency reliability of the BSCI was examined by computing Cronbach's alpha and the omega coefficient using SPSS version 27 (IBM Corp., Armonk, NY, USA). To assess the BSCI's construct validity, theory-driven correlations between BSCI scale scores (sum of items) and main study variables were examined. The analyses were conducted in Mplus using RFIML. We also computed correlations between main study variables and SCS-SF total scores, SCS-SF positively worded items (summed), and SCS-SF negatively worded items (summed). We then examined whether the BSCI had smaller correlations with negative psychological variables, such as anxiety and depressive symptoms and rumination, compared to the SCS-SF total score. Additionally, we examined whether the BSCI had smaller correlations with anxiety and depressive symptoms compared to negatively worded SCS-SF items. To determine whether the correlations were significantly different, we first converted the correlations into zscores using Fisher's r-to-z transformation and then used a z-test to test the significance [63].
Measurement invariance. Given our focus on creating a generalizable measure, we tested measurement invariance of the BSCI across cancer stages, cancer types, and genders. Invariance models were tested in stepwise order, starting from the least restrictive level to the most restrictive level. The first level, the configural invariance model, imposes the same factor structure simultaneously across the groups without any parameter constraints. The second level is the metric invariance (weak invariance) model, where factor loadings are constrained to be equal across the groups. The third level is scalar invariance (strong invariance) where both factor loadings and intercepts are constrained to be equal across the groups. Finally, the fourth and most restrictive level is the strict invariance model where factor loadings, intercepts, and error variances are all constrained to be equal across the groups. Again, RFIML was used for all the models and scaled Satorra-Bentler chi-square difference tests [64] were conducted to compare the models. A nonsignificant chi-square difference test indicated that the more restricted model was preferred.

Results
Of the 701 patients who received recruitment materials, 109 were not reached, 29 were ineligible, 99 declined, and 60 did not complete the survey or were omitted from analyses (e.g., survey returned with significant missingness), leading to a sample size of 404. Sample characteristics are found in Table 1. Results for the initial 15-item SCI, including item selection, factor structure, reliability, and validity, can be found in the S4-S10 Appendices. Code for all analyses in this paper and the appendices can be found in the S11 Appendix.

Item selection and factor structure
The five items with the highest item-total correlations were retained for the BSCI. The five selected items also met face validity, reflecting the main facets of self-compassion-self- kindness, common humanity, and mindful acceptance. Given that a single factor structure was best for the 15-item measure, we fit a single factor model to the BSCI. The model had a better model fit (SRMR = 0.03, CFI = 0.98, RMSEA = 0.07) than all models tested with the SCI. The BSCI and SCI scale scores were highly correlated (r = 0.94). Item-total correlations and interitem correlations were also examined (see Table 2), and no problematic items were found. All standardized loadings exceeded the recommended cut-off of 0.40 (range = 0.76-0.83, see Table 2). Internal consistency reliability was excellent (α = 0.90; ω = 0.90).

Invariance testing of the BSCI
Measurement invariance testing results are found in Table 4.

Discussion
This study aimed to develop and evaluate the psychometric properties of a new self-compassion measure, the BSCI. Findings support the BSCI's unidimensional factor structure and excellent psychometric properties. Furthermore, results suggest strict invariance of the BSCI across cancer stages, cancer types, and genders, indicating psychometric equivalence for use across subgroups. To date, most self-compassion research has used the SCS or SCS-SF, which have conceptual and psychometric limitations [5,6,65]. Other self-compassion measures have limited evidence of validity [30]. Overall, the BSCI addresses limitations of existing self-compassion measures and will help advance self-compassion research.
The unidimensional factor structure of the BSCI may have emerged for multiple reasons. In contrast to the SCS [2], our items reflected a standard conceptualization of mindfulness that may be more highly correlated with other facets of self-compassion. The omission of negatively worded items also may have contributed to our measure's unidimensional structure. Although negatively worded items are thought to prevent acquiescence bias (the tendency to overendorse items), these types of items have not been found to prevent this bias [66]. In fact, negatively worded items may lead to errors due to careless responding or elicit a different response pattern than positively worded items [67,68]. Research suggests that if 10% show careless responses to such items, a unidimensional structure is likely to be rejected [68].
Construct validity of the BSCI was supported through its correlations with theory-driven psychological variables. Consistent with theory [39], the BSCI was positively associated with the mindfulness facets of nonreactivity, nonjudging, and acting with awareness. Further evidence of construct validity included the BSCI's positive associations with peaceful acceptance of cancer and progress in values-based living and negative associations with their counterparts, struggle with illness and obstruction in values-based living. Findings are consistent with theory suggesting that acceptance of cancer requires one to turn towards this difficult experience with kindness rather than attempting to avoid it [69]. Theory also suggests that greater self-compassion will result in prioritizing actions that benefit the self, such as living more consistently with personal values [10,70]. In addition, greater self-compassion on the BSCI was related to higher levels of active coping, less denial, and better quality of life, which converges with prior research [71].
Regarding "negative" psychological variables, the BSCI was inversely associated with rumination, psychological inflexibility, and cognitive fusion. The inverse link between self-compassion and rumination is consistent with prior research with cancer populations [17]. In addition, people with low self-compassion may judge or criticize their thoughts and feelings rather than recognize the universality of such experiences. According to contextual behavioral theory, this judgment of internal experiences is associated with greater cognitive fusion or entanglement with thoughts and psychological inflexibility [10]. This inflexibility emerges when people attempt to avoid difficult experiences, resulting in behaviors inconsistent with personal values (e.g., avoiding family gatherings in fear of others asking about their cancer).
Consistent with predictions, associations with "negative" psychological constructs (e.g., rumination, denial) were 1.6 to 2.2 times as large for the SCS-SF total score compared to the BSCI, with most associations being close to twice as large. This pattern of findings appeared to result from negatively worded items in the SCS-SF. Indeed, negatively worded items in the SCS-SF had significantly larger correlations with anxiety and depressive symptoms compared to the BSCI. Thus, the BSCI addresses an important limitation of the SCS-SF and SCS, as items do not have inflated correlations with psychopathology.
Strict measurement invariance was established for the BSCI across cancer stages, cancer types, and genders, suggesting that observed differences in self-compassion between subgroups most likely reflect true group differences rather than the result of biased measurement. Thus, the BSCI is acceptable for use with adults with varying cancer stages (early, advanced), cancer types (breast, gastrointestinal, lung, and prostate cancer), and genders and can be used to make meaningful comparisons between these subgroups.
Limitations of this study should be noted. Although purposive sampling based on National Cancer Institute data ensured more representation of racial and ethnic minority individuals, the majority were non-Hispanic white, reflecting the demographics of our recruitment sites in Indiana. In addition, this study was cross-sectional, which did not allow for an examination of test-retest reliability. Furthermore, to reduce participant burden, other constructs for the validity analyses were not assessed, such as self-criticism and compassion for others. Finally, levels of anxiety and depressive symptoms in our sample were low compared to cancer patient norms [72]. Among cancer patients, lower distress is correlated with lower symptom burden and better adjustment [73].

Conclusions
In conclusion, improving the measurement of self-compassion is necessary for advancing science. By following gold-standard practices for measure development and testing [44,74,75], this study produced a new 5-item self-compassion measure, the BSCI, with robust psychometric properties. The BSCI was found to be acceptable for use across samples of varying cancer stages, cancer types, and genders. Next steps include testing the BSCI with more culturally diverse cancer populations as well as other medical and nonclinical populations. In addition, the BSCI could be tested as a mediator of compassion-focused or mindfulness-based interventions' effects on psychological and physical health outcomes. Overall, use of this brief measure will reduce participant burden, improve the validity of self-compassion measurement, and allow for examination of theory underlying compassion-focused interventions.